The present invention relates to a magnetron for an electronic range for generating a microwave, and more particularly to a condenser unit for the magnetron, wherein the unit has a condenser mounting plate capable of preventing the leakage of microwave through the connecting portion of the condenser mounting plate and a filter box of the magnetron.
A magnetron for an electronic range is a kind of an electron tube which has been adapted for generating microwave energy, at generally high frequency, for defrosting and heating articles of food by means of dielectric heating thereof. A known magnetron has a conventional structure as shown in FIGS. 1 and 2, which are a partially sectioned elevational view of the known magnetron and a partially side-sectioned view showing the connection of the penetration-type condenser with the filter boxes of the magnetron of FIG. 1, respectively.
As shown in FIGS. 1 and 2 of the drawings, a conventional magnetron generally comprises a housing 11 having a filament 1 for emitting thermions, the thermions being "thermal electrons" which are emitted from a solid body by being excited with a thermal energy when metal or semiconductor is heated at a very high temperature. The magnetron generally also comprises an anode vane 2 to which the thermions from the filament 1 are directed, a permanent magnet 3 for rotating and accelerating the thermions, a radiating antenna 4 for radiating high-frequency electromagnetic wave energy, a plurality of radiant tubes 5 each adapted to radiate heat generated from the anode vane 2 in order to cool the anode vane 2, a lead 6 for leading electric power to the filament 1, a choke coil 7 for dumping conductive noise emitted from the lead 6, a penetration-type condenser 8 adapted for improving the dumping efficiency of the conductive noise in cooperation with the choke coil 7 and functioning as a terminal for facilitating the application of electric power from the power source, and upper and lower filter boxes 9 and 10 each adapted to shield radiation noise emitted from the lead 6.
The microwave energy generated by the above-mentioned magnetron has a frequency of about 2450 Mhz and is radiated at the radiating antenna 4 of the magnetron toward the cooking chamber of the electronic range.
On the other hand, the high-frequency electromagnetic wave will also be applied to the input part comprising the filament 1 and the lead 6, simultaneously with being applied to the radiating antenna 4.
The high-frequency electromagnetic wave applied to the lead 6 has been generally denoted as the conductive noise, while the electromagnetic wave radiated from the lead which functions as if it was an antenna radiating into the space of the input part, has been generally denoted as the radiation noise.
Each of the above-mentioned two-types of noise is emitted from the magnetron so as to cause interference in television or communication machinery.
Most of the conductive noise emitted from the input part of the magnetron toward the outside could be prevented by the choke coil 7 and the penetration-type condenser 8, and also the radiation noise emitted from the lead 6 into the inner space of the input part could most likely be prevented by sealing tightly both upper and lower filter boxes 9 and 10, the filter boxes 9 and 10 covering the inner space of the input part.
The upper filter box 9 is necessarily provided with a condenser receiving opening 9b at the center of a front panel thereof and a plurality of mounting holes 9a, the mounting holes 9a being arranged around the receiving opening 9b, because the upper and lower filter boxes 9 and 10 must be assembled with other parts such as the condenser 8 so that the upper and lower filter boxes 9 and 10 are necessarily formed to be separate from one another as shown in FIG. 3. In assembling the upper filter box 9 to the condenser 8, each mounting hole 81a formed in the mounting plate 81 of the condenser 8, in order to correspond to each mounting hole 9a of the upper filter box 9, is first inserted onto each burring protrusion 9a.sub.1 formed to integrally extend from each mounting hole 9a of the upper filter box 9 as shown in FIG. 4, and thereafter, each burring protrusion 9a.sub.1 is pressed by means of a pair of pressing jigs j.sub.1, j.sub.2 in order to tightly mount the condenser 8 to the upper filter box 9 as shown in FIG. 5 so that there is inherently a gap G between the front surface of said mounting plate 81 of the condenser 8 and the bent rear surface of a burring plate portion 91 of the upper filter box 9, the gap G inherently formed as the burring plate portion 91 of the upper filter box 9 is gently bent upon the depression of each burring protrusion 9 during the burring process by means of the pressing jigs j.sub.1, j.sub.2. In an effort to remove the bending gap G, an assembly method has been proposed in which the burring plate portion 91 of the upper filter box 9 is previously bent in the opposite direction before the burring process, and then the burring protrusions 9a.sub.1 are each pressed by the pressing jigs, thereby making it possible to remove the gap G by offsetting the press bending effected by the previous opposite bending. However, it is known that the assembling method has disadvantages of difficulty in calculating the bending dimensional tolerance. The dimensional tolerance may be obtained from repeated experiments, and furthermore, there is a limit in providing the perfect sealing condition for the upper and lower filter boxes 9 and 10.
In addition, it is known that there is another disadvantage because of the bending gap G, such as leakage of large quantity of frequencies of the fifth higher harmonic therethrough, the fifth higher harmonic having a considerably shorter wave length than that of the basic frequency and causing problems such as in the reception of satellite communication to occur.